Purple underneath seedling leaves, then they curl up and die

[z_willus_d]

Hello,

I apologize for the abruptness of this post, but I'd just finished typing up a good one and my computer ate it. It ate a good deal of my patience at the same time.

My situation is as follows. I have 40 seedlings that are of various ages, mainly around 2 weeks old since transplanting up to 6" pots. The vast majority of the seedlings are exhibiting an deep purple color on the underside of their leaves. I've had this in the past and it's never been an issue (not major in any case). I've read it might have something to do with phosphate uptake issues, which can have to do with (a) no phosphate or (b) cold soil temps or (c)...? In any case, I've got very warm temps in my grow room (68F-85F) and I'm using what I've read is fairly rich FoxFarms Ocean Forest /Floor potting mix (1 part Light Warrior, 3/4 part Ocean Floor).

I wouldn't write this thread if it were only a problem of purple (underside) leaves, but it's more than that. Yesterday I noticed wilting on the first set of true leaves on one of my seedlings, and within 1-2 hours those leaves (/w branch) had curled up and atrophied from the main stem. Since then, five more plants have followed suit. The rest of the plant seems healthy, but this scares me.

I've attached pics showing this condition on a couple of the seedlings. I'm afraid the problem will move on up to the next set of leaves and so on. Any ideas what this could be? Should I do something? If so, what?

Note, until this morning I hadn't added any fertilizer or additives, other than an application of Actinovate/MycoGrow/BiotaMax (all mycos) and Roots Excelurator. Those are all quite benign. This morning, I watered with a very dilute fish/kelp extract, hoping to perhaps add some N and P to the mix. I leave an oscillating fan directed at the seedlings for 1/2 the light day, which is currently set at ~16-18 hours a day (dark the rest).

Any questions I can answer to help diagnosis this syndrome, please let me know.

Thanks all!
-naysen